Credit: Axel Aitoff - people.physics.tamu.edu · perigalacticon distance of 1.8 x 1013 m = 120 AU...
Transcript of Credit: Axel Aitoff - people.physics.tamu.edu · perigalacticon distance of 1.8 x 1013 m = 120 AU...
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Credit: Axel Aitoff
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Milky Way Galaxy
Our Galaxy is a collection of stars and interstellar matter - stars, gas, dust, neutron stars, black holes -
held together by gravity
Composite near-IR (2 micron) Image from the Two Micron All Sky Survey (IPAC/Caltech/UMass)
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The Morphology of the Galaxy
The solar Galactocentric distance, R0, is still debated. In 1985 the International Astronomical Union (IAU) adopted R0 = 8.5 kpc. Recent studies
find R0 = 8 kpc (Eisenhauer 2003). Your book uses this latter value.
The Galaxy is composed of a bulge, a thin and thick disk, and a halo.
Most stars are in disk components. Disk contains lots of gas and dust.
Halo has low density and it contains many globular clusters.
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Milky Way Galaxy
The Galactic Bulge
COBE Satellite image of Milky Way at 1.2-3.5 micron.
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from Digital Sky LLC
Spiral Structure
Galaxy M 51
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Morphology of the Milky Way
from Digital Sky LLC
Sun
R0 = 8 kpc
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from Digital Sky LLC
http://www.youtube.com/watch?v=Suugn-p5C1M
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The Galactic Center
Challenging to observe because of all the dust/gas !
But, in 15 million years, the Sun will be 85 pc above the Galactic midplane, we would presumably have a much better view then !
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The Galactic Center
Astronomers use high angular resolution images in the near-IR (~2 micron) to help see through the dust. This is helpful because
there are large number of K and M giant stars (T ~ 4000 K) in the central part of the galaxy, and
these are brightest in at 2-micron.
Note that the nearest star to the Sun is ~1 pc away. The density of
stars is much higher in the Galactic Center !
From Schödel et al. 2002
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The Galactic Center
Astronomers use high angular resolution images in the near-IR (~2 micron) to help see through the dust. This is helpful because there are large
number of K and M giant stars (T ~ 4000 K) in the central part of the galaxy, and these are brightest in at 2-micron.
Astronomer group led by Rainer Schödel and Reinhard Genzel followed the orbits of K-giants near the Galactic center.
One star, S2, has a period of 15.2 yr with eccentricity e=0.87 and perigalacticon distance of 1.8 x 1013 m = 120 AU (a few times bigger than
Pluto’s orbit).
You can work out from Kepler’s laws that the mass interior to S2’s orbit is ~3.5 x 106 solar masses.
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The Galactic Center
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The Galactic Center
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The Galactic CenterProf. Andrea Ghez’s UCLA group.
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The Galactic Center
Nature, Vol. 419, p. 694 (2002)
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The Galactic Center
Nature, Vol. 419, p. 694 (2002)
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The Galactic Center
Degeneracy between distance to center of Galaxy and Mass
of supermassive blackhole
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What would happen to a star that ventures too close to the Galactic Supermassive Blackhole?
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http://arxiv.org/pdf/1205.0252v1.pdf
What would happen to a star that ventures too close to the Galactic Supermassive Blackhole?
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What would happen to a star that ventures too close to the Galactic Supermassive Blackhole?
Gezari et al. (2012, Nature): http://arxiv.org/pdf/1205.0252v1.pdf
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What would happen to a star that ventures too close to the Galactic Supermassive Blackhole?
http://arxiv.org/pdf/1205.0252v1.pdf